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rsterne · Moderator

I just assembled a 1750 out of parts today.... thanks to AirGunEric for the Crosman parts, and ustilago for a DPH and barrel band.... 18" .177 barrel, steel breech, bone stock except for the DPH.... All testing was done with JSB Express, 7.9 gr. pellets.... at a temperature of 60*F.... Wink

I found that the DPH has basically 10 turns of usuable adjustment from coil bound on the spring to as low as my chronograph will measure, which indoors with the light kit seems to be about 150 fps.... I called the setting near coil bound "Power 10", and all the way out "Power 0".... I got a pretty smooth velocity curve with the hammer on the low power setting.... On high power, there was basically no difference in velocity except with the adjuster loosened right off.... The high power velocities were taken with the cartridge down about 5-20 shots, and all velocities are the average of 5 shots :

Low Power 0: 170 fps
Low Power 1: 245
Low Power 2: 310
Low Power 3: 350
Low Power 4: 390
Low Power 5: 425
Low Power 6: 462
Low Power 7: 485
Low Power 8: 505
Low Power 9: 523
Low Power 10: 540

High Power 0: 550 fps
High Power 1: 581
High Power 2: 588
High Power 3: 591
High Power 4: 593
High Power 5: 595
High Power 6: 597
High Power 7: 599
High Power 8: 602
High Power 9: 604
High Power 10: 599

What I did notice was that as you increased the power setting on high power (from High Power 2 and up), the gun just got noiser and used more gas.... Rolling Eyes

After looking at the numbers, I set the velocity adjuster to "power 7" so that on low power it would be just under 500 fps.... Then I shot one complete cartridge at high power, and another at low power.... the difference AMAZED me:

On High Power 7, the first 10 shots hovered aboud 600fps.... then dropped over the next 10 shots to about 570, where they stayed until about 35 shots, when it started to decrease again until it was 551 at 44 shots, and then dropped to less than 300 fps by shot 54.... Basically, there were 44 good shots averaging 575 fps (high of 605 and low of 551).... and the total energy realized over 54 shots was 290 FPE....

On Low Power 7, there was no initial surge of velocity.... I broke it up into groups of 20 shots in the summary below:

1-20 shots: High 494 fps, Low 470 fps, Average 482 fps
21-40 shots: High 496, Low 473, Average 483
41-60 shots: High 490, Low 467, Average 478
61-80 shots: High 494, Low 472, Average 484
81-100 shots: High 492, Low 474, Average 484
101-120 shots: High 492, Low 478, Average 485
121-140 shots: High 495, Low 466, Average 485

The next ten shots saw the velocity fall to 300 fps.... There were basically 140 good shots that averaged 483 fps (high of 496 and low of 466), and the total energy realized over 150 shots was 604 FPE.... more than DOUBLE what I got on the high power 7 setting.... Shocked

I am EXTREMELY pleased with how efficient this gun is with ustilago's Dual Power Hammer (DPH).... I would strongly recommend it to anyone who is interested in doing lots of shooting cheaply, while maintaining the ability to crank up for a "kill shot" whenever you feel like it.... Cool

Bob

broommaster2000 · Moderator

I don't think you're rifle is doing that much foot pounds of energy. Mr. Green

That's more then a 9mm. Wink

rsterne · Moderator

I hope you're just kidding.... Rolling Eyes

that's the TOTAL energy of all 150 shots.... something like 86% of the 700 FPE theoretical energy available in a 12 gram CO2 cartridge.... Shocked

Bob

AirGunEric · Site Admin

Broom's just fooling about- English is also his second language.

That being said, I am amazed at the low power results- 140 shots averaging 483fps at 7.9gr

It also shows what can be accomplished with proper hammer/valve balancing.

Looking at those results at only 60*F- at 70*F, mathematically speaking, your average velocity on that setting could very well have been 14% higher, or 550fps. That is indeed impressive.

rsterne · Moderator

Actually, I'm in the middle of testing the effect of temperature right now.... The second set of results, at 45*F, show that at the lowest power levels, the velocity INCREASES at the lower temperature.... The curves cross over at about 500 fps and all the velocities at the High Power hammer settings are less, in the 550-560 fps range (as they should be).... Shocked

It would appear that what is happening is that the valve/hammer are becoming self regulating when the DPH is used in the "economy" mode.... At lower temperature (and CO2 pressure), the valve is easier to open.... and at very low power settings, the valve is opening further and for a longer time, permitting more gas to escape and actually increasing the velocity:

On Low Power #1, I was getting 296 fps at 45*F vs only 245 fps at 60*F....
On Low Power #4, I was getting 417 fps at 45*F vs. 390 fps at 60*F....
On Low Power #7, the results were pretty much equal (493 & 485)....
On Low Power #10, I was getting 521 fps at 45*F vs 540 at 60*F....

I am trying to get the temperature in my garage to 75*F to do another set of tests.... I expect to see the reverse occuring.... with the three curves crossing somewhere around 500 fps.... I had a theory going into this project that it might be possible to come up with a hammer setting that would self-regulate over a pretty wide range of temperature.... it looks like my theory is about to be proven.... Wink

Bob

Slavia · Moderator

Nice work! The two points that I find most interesting are: 1. Using total FPE rather than just number of shots to measure efficiency, and 2. Being able to compensate for temperature differences.

I have a 2240, but I don't consider myself a CO2 guy. How did you come up with the (theoretical) 700 FPE per CO2 cylinder?

AirGunEric · Site Admin

For anyone not familiar with this "DPH" (Dual Power Hammer), here is a picture of it (used on Crosman Co2 22/17xx platform guns):

Doc Sharptail · Member

Where is the sweet-spot on this thing, in terms of shot to shot velocity consistency? I'm guessing it would be around setting 7 or 8 on the low power side.

In my brief .177/Co-2 experimenting on a 22-40 base, I could not get tighter than a 35-40 fps shot to shot variation- and it showed at the 15M board groups.... I did little in the way of valve modding- zero actually. Temperature may have been a part of it too- the powerlet is not at it's best at 58F....

Regards,

Doc Sharptail

rsterne · Moderator

The 700 FPE is from a post by SinNC.... have no idea where he got the number....

and yes, the sweet spot seems to be about 7 or 8 on low power.... if I can ever get my garage to 75*F I'll do another series....

Bob

DerekVinyard · Member

I have a DPH on my favourite target pistol. Once you get one, you want them on all your 22xx airguns. It's a dream on the 1377 as well.

rsterne · Moderator

OK here you go.... bear in mind it's not finished.... Rolling Eyes

I couldn't get my shop to 75*F today (it's -15*C outside).... so I had to settle for 68*F.... That at least gave me three temperature curves with the different DPH settings, and indeed they all cross over at about "Low Power 8".... ie about 2 1/2 turns out from coil bound on the spring, and using the "economy" setting (first click).... I didn't test every setting at 45*F and 68*F like I did at 60*F.... but the results speak for themselves.... Cool

Over the range of temperatures from 45*F to 68*F, and using "Low Power 8", the gun is self-regulating.... ie temperature no longer makes a difference.... I hope to eventually test at about 30*F and 75-80*F and determine if it still holds true.... but even if it doesn't, I think I've accomplished something pretty new here.... a CO2 gun that isn't sensitive to temperature.... Shocked

I decided to expand on the shot strings I did the other day, and since 68*F (20*C) is a pretty typical temperature for CO2, I tested shot strings at four DPH settings:

High Power 10: 614 fps average (655 high, 586 low) - 37 good shots - 289 FPE total energy over 48 shots to 300 fps.
High Power 4: 620 fps average (648 high, 581 low) - 60 good shots - 458 FPE total energy over 74 shots to 300 fps.
High Power 1: 573 fps average (592 high, 552 low) - 86 good shots - 551 FPE total energy over 101 shots to 300 fps.
Low Power 8: 500 fps average (517 high, 484 low) - 125 good shots - 577 FPE total energy over 135 shots to 300 fps.

Some things of note:

High Power 4 was better than "wide open".... flatter shot string, higher average velocity, 60% more total energy....
At High Powers 10 and 4, the "knee" on the velocity curve where I stopped counting good shots was over 10% lower than the maximum velocity.... while at High Power 1 and Low Power 8, the "knee" was only down 6-7%.... ie more consistency....

Low Power 8 was extremely consistent throughout the shot string.... I broke the shot string in four groups of 30:

Shots 1-30: 501 fps average (517 high, 490 low)
Shots 31-60: 500 fps average (512 high, 486 low)
Shots 61-90: 500 fps average (513 high, 488 low)
Shots 91-120: 501 fps average (514 high, 485 low)

This phase of testing is now complete.... I have achieved 125 shots at 500 fps for a total energy of 549 FPE over those 125 shots, with 7.9 gr. JSB Express .177 cal at 68*F.... In addition, the velocity is constant over the range of temperature from 45*F to 68*F, and probably more.... By cocking the DPH to the "kill" setting, the velocity jumps to about 630 fps.... I will now be enlarging the transfer port slightly to see what effect that has on the results.... If that works, then the barrel port will get a slight tweak as well.... Twisted Evil

Bob

AirGunEric · Site Admin

I'm starting to get all hot on the idea of installing a DPH now- I shot off about 100 shots on a 2240 using a .177 10.1" barrel and it ran out of gas, twice- which is about $2.00 worth of Co2. It appears if I had the DPH installed I might be out 75 cents in Co2 for the same shooting and have a nice 500-ish fps output for shorter range targeting.

Hmmm...

broommaster2000 · Moderator

Bob,

Why would anyone want to know the total amount of energy from a CO2 cartridge? Doesn't it matter only how much energy is translated by each pellet? Doesn't it fluctuate to much depending on energy?

ustilago · Member

The amount of energy extracted from a powerlet is a measure of efficiency.
The cool thing about that is, it blows SiNC's efficiency out of the water :D

In Power mode most of the "lost" CO2 results in loud noise and no extra velocity. Bob didn't comment on it but in "economy" (low power) mode the report is. . . clipped. It's a sharp CRAck! Instead of the CR-R-R-R-R-R-R-R-ACK! that a 2240 owner is used to (ok, that might be slightly exaggerated, just a little bit).

is it 3am already? Geez, I gotta be up in 4 hours to get the kidlets off to school. . .

Alstone · Moderator & Site Supporter

Nice bit of comparison between the different settings Bob I get similar results from my QB78 using the power adjuster, on high power it also tends to blow excess gas out of the barrel.

On another of my guns I have fitted an extra weight on the hammer, as against increasing the spring pressure, and I find that when the temperature is high the fpe increases considerably, due to the hammer weight, but when used at low temperature the FPE falls off and the extra weight just blows excess gas out the barrel, but if I remove the weight the FPE increases, the cross over point is aroung 450fps. What I need is an adjustable hammer weight that can be set easily, and I think a combination of a DHP and adjustable Hammer weight, you could cover all shooting scenarios?

I hope this makes sense, BTW I like he chart.

Al